I can’t seem to find the option in Kodi 17 (using the default theme). Back in Kodi 16 (Confluence skin?) there was an option on the left menu to hide watched episodes/movies but I can’t find it now.
I have spent a couple of days trying to search for this and all I have found are posts about marking as watched, something about sending keypresses or similar, but aside from one unanswered reddit post nothing about it, so I apologise if it has been answered but I haven’t been able to find the answer 
My partner is getting annoyed at me for upgrading LOL